1. Field of the Invention
The present invention relates to resin encapsulation systems used for subjecting semiconductor devices to resin encapsulation molding and, more particularly, to a resin encapsulation system using three plastic molds: an upper mold, a middle mold, and a lower mold.
2. Description of the Related Art
This kind of resin encapsulation system is used in a process for encapsulating semiconductor chips, which are cut from wafers in several manufacturing processes for semiconductor devices, in mold resin. In order to manufacture semiconductor devices with high efficiency, the efficiency of the resin encapsulation molding process must be improved.
To be more specific, the resin process can be subdivided into a step of releasing an object encapsulated with resin from a mold, a step of releasing a runner and a gate from the mold and a process to clean the middle mold. In order to improve the efficiency of the resin encapsulation process, these steps should be done automatically and rapidly.
Referring to FIG. 1, this kind of resin encapsulation system generally uses an upper mold 602, a middle mold 601, and a lower mold 603. Since, the middle mold 601 is connected with both the upper mold 602 and the lower mold 603 via links 604, the middle mold 601 moves according to movement of the upper mold 602 and the lower mold 603.
In Japanese Unexamined Patent Application Publication No. 153506/1997 and No. 314717/1994, a three-mold structure including upper, middle, and lower molds are disclosed. FIGS. 2A and 2B refer to typical views disclosed in Japanese Unexamined Patent Application Publication No. 314717/1994 and the details are described below.
FIG. 2A is a perspective view of a mold-releasing load-measuring mold disclosed in Japanese Unexamined Patent Application Publication No. 314717/1994, and FIG. 2B is a sectional view thereof.
As shown in the drawings, the mold-releasing load-measuring mold is formed of an upper mold 701, a middle mold 702, and a lower mold 703.
A resin injection hole 704 formed in, e.g., a circular truncated cone shape, is formed in the upper mold 701 communicated with a resin input port 706 of a transfer molding machine 705.
A cavity portion 709, a runner portion 707, and a gate portion 708 are formed on the middle mold 702 to allow the runner portion 707 to communicate with the cavity portion 709 via the gate portion 708.
A mold-releasing load-measuring method using the mold-releasing load-measuring mold is described in detail below.
First, the mold-releasing load-measuring mold is clamped by, e.g., a pressing force of a cylinder, while laminating the upper mold 701 and the lower mold 703 on the upper and lower faces of the middle mold 702, and then, is input in this state, a mold resin 716 made of, e.g., thermosetting resin, into the resin input port 706 of the transfer molding machine 705.
Then the input mold resin 716 is injected inside the cavity portion 709 via the gate portion 708 while heating the mold resin to melt it.
When the cavity portion 709 and a penetrating hole 712 are filled with the mold resin 716 (see FIG. 3), the resin is made to harden by thermal changes such as heating or cooling.
Then the upper mold 701 and the lower mold 703 are opened to remove only the middle mold 702, as shown in FIG. 3, and pressure is applied to a pressing part 717 provided in the penetrating hole 712 in a predetermined direction, that is, from an exposed surface of the pressing part 717 toward the cavity portion 709, as indicated by arrow B in the figure, by a measuring apparatus such as a spring balance.
Finally, the mold resin 716, which adheres to both side faces 710 and a flat surface 711 of the cavity portion 709, is released from the middle mold 702 by the load acting on the pressing part 717. By reading a scale on the measuring apparatus at that time, the load when the mold resin 716 is released from the middle mold 702 is measured.
Including the above-described examples, this kind of resin encapsulation system in the conventional art has some problems, as described below.
A hollow gate is adopted for the middle mold. Therefore, although it is physically possible to mount an eject mechanism for the gate portion inside a molding press, it is not practical considering procedures and efficiency (called the ‘index’) of a series of resin encapsulation processes and equipment costs. In other words, it is inappropriate for mass production facilities.
A cleaning mechanism is usually provided in order to remove burrs that remain on the plastic mold after each resin encapsulation. In the three-mold structure, the cleaning mechanism is much too complicated to be practical considering the index and the equipment costs described above and is inappropriate for mass production facilities.
Moreover, since, in the three-mold structure of the conventional art, each mold is fixed by the link described before, maintenance is time-consuming and lowers the productivity, which is a problem.
The mold-releasing load-measuring mold described in FIGS. 2A and 2B is subdivided into three molds: the upper mold, the middle mold, and the lower mold and the cavity portion is formed in the middle mold. However, since there is no machining provided on the middle mold where a conveying mechanism can easily grip it, the conveying mechanism cannot easily remove and insert the middle mold from between the upper mold and the lower mold.